1. Field of the Invention
The present invention relates to a thread-wound golf ball with a center, a rubber thread layer covering the center, and a cover. More specifically, the present invention relates to a thread-wound golf ball that exhibits great carry distance with good shot feel and that easily comes to a halt with high spin rate when shot from the rough or when shot in the rain.
2. Description of the Background Art
The basic structure of a thread-wound golf ball includes a rubber thread layer formed by winding a rubber thread on a solid center of a solid rubber or a liquid center with a liquid covered with a rubber, and a cover formed around the rubber thread layer.
Thread-wound golf balls formed of a balata cover and a liquid center are widely used by low-handicapped golfers and professional golfers, providing excellent shot feel and controllability.
However, the structure of such golf balls are inferior to those formed of an ionomer resin cover and a solid center in flight performance, cut resistance, and durability. Further, the use of the liquid center has a disadvantage that the fabrication process is difficult and, if the ball is cut with a cutter or the like, the inside liquid may spray out. If the liquid comes into eyes, one would possibly lose one""s sight.
On the contrary, a thread-wound golf ball formed of a balata cover and a solid center has advantages over that of the balata cover and the liquid center in that it is fabricated by a simple process and that it assures safety in case that the ball is damaged.
However, the golf ball of the solid center is inferior to that of the liquid center in that spin rate is so high and hitting angle is so small that carry distance is extremely reduced.
For example, U.S. Pat. No. 5,397,129 has proposed a thread-wound golf ball including a rubber thread layer formed by winding a rubber thread onto a solid rubber center of, e.g., silicone rubber, having a prescribed surface hardness and compressibility, and a cover layer formed on the rubber thread layer.
The aforementioned U.S. Patent provides for lower spin rate and greater hitting angle to achieve a prescribed carry distance.
However, the aforementioned laid-open application suffers from a problem that sufficient spin rate is not achieved when shot from the rough or in the rain, whereby a ball does not easily come to a halt.
On the other hand, U.S. Pat. No. 5,716,293 has proposed a thread-wound golf ball directed to provide a golf ball with excellent shot feel, controllability, flight performance, durability, and cut resistance. The golf ball includes a solid center formed of an inner core rubber portion containing a vulcanized rubber composition of an oily substance and a cover layer formed on the inner core rubber portion, a rubber thread layer, and a cover mainly including ionomer resin with a stiffness modulus of 70-280 MPa.
The aforementioned laid-open application provides good shot feel and increased spin rate when shot by a short iron. In addition, the use of a solid center alleviates the problem of difficult fabrication process as compared to the case of the liquid center.
However, the aforementioned invention still suffers from the problem associated with difficult fabrication process because of the center of a two-layer structure. Further, the spin rate in a wet condition is inferior to the spin rate in a dry condition. Therefore, these golf balls were not satisfactory also from the aspect of spin maintenance.
The present invention is made to solve the aforementioned problems. An object of the present invention is to provide a thread-wound golf ball, such as a balata-covered golf ball, that exhibits great carry distance with good shot feel and that can easily come to a halt with high spin rate when shot from the rough or when shot in the rain.
The above object is achieved by a golf ball of the present invention set forth in the following.
According to an aspect of the present invention, a thread-wound golf ball is constituted by a center, a rubber thread layer covering the center, and a cover. The center has a diameter of 28-35 mm and a Shore A hardness of 10-50. The cover is formed of a mixture containing ionomer resin, thermoplastic elastomer, and tackifier, and has a Shore D hardness of 45-60.
According to another aspect of the present invention, a thread-wound golf ball includes the above center, where the center is formed of a cross-linked mold mainly containing silicone rubber.
According to still another aspect of the present invention, the thermoplastic elastomer of the thread-wound golf ball contains at least one of a styrene-butadiene-styrene block copolymer (SBS structure), a modified product thereof, or a hydrogenate thereof.
According to still another aspect of the present invention, the thermoplastic elastomer of the thread-wound golf ball contains at least one of a styrene-isoprene-styrene block copolymer (SIS structure), a modified product thereof, or a hydrogenate thereof.
According to still another aspect of the present invention, the tackifier of the thread-wound golf ball contains at least one of terpene resin and rosin ester.
According to still another aspect of the present invention, the tackifier of the thread-wound golf ball has an SP value of 7.0-10.0.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.